In a seat structure such as a seat for vehicle, a headrest is provided in a seat back. As shown in Patent Documents 1 and 2, normally, the headrest is composed of polyurethane foam that is supported by a headrest frame and has a thickness of a few cm to 20 cm in a front and back direction and a width of around 20 to 30 cm. In addition, such headrest is manufactured by providing the headrest frame as a core member, in a skin member formed in a bag shape, injecting a polyurethane foam raw material, and performing integral foaming with the skin member.